1. Field of the Invention
The present invention relates to a light source device. In particular, the present invention relates to a light source device used in an image reading device or the like which, by an optical system, focuses light which has passed through an original onto an image pick-up device, and which photoelectrically reads the image information of the original.
2. Description of the Related Art
Devices have been widely used which form images on recording materials as follows: the device carries out image processing (such as enlargement or reduction of an image, correction of missing portions of the image caused by scratching of the film or the like) on digital image data which is read by using an image reading device which, by an optical system, focuses a ray, which has passed through a frame image recorded on an original such as a photographic film, onto an image pick-up device such as a CCD or the like, and photoelectrically reads the image information of the frame image. The device forms an image on a recording material by laser light which has been modulated on the basis of the digital image data which has been subjected to the image processings.
There have conventionally been such image reading devices which read an image of a photographic film, which is set at a film carrier disposed on a carrier stand provided at a table, by an image pick-up unit disposed above the table of the device main body. The image pick-up unit focuses the image of the photographic film onto an image pick-up device at a necessary magnification by a lens unit.
Ternary light-emitting diode (LED) elements which emit lights of red (R), green (G) and blue (B), and LED elements emitting infrared rays (IR) which are invisible light which is non-responsive to these color wavelengths (i.e., non-responsive to image information of wavelengths in the visible light region) are provided below the carrier stand as the light source device. An LED light source, which is structured by these elements being distributed and arrayed uniformly on a flat surface of a single substrate, is provided, and a filter and a diffusion box are provided above the LED light source. The luminous flux of the light emitted from the LED light source, which is modulated at the filter and thereafter being diffused within a predetermined range in the light-diffusing box, passes through the photographic film which is set within the film carrier on the carrier stand, and is projected onto the image pick-up unit.
When an image is read by an image reading device having the above-described structure, the light emitted from the LED light source passes through the film, is condensed at the lens of the lens unit, and is focused on the CCD, and the image data is read.
There are cases in which missing portions arise on the image when the film surface is scratched or when the image is affected by dust or the like existing on the optical path from the light source to the film (hereinafter, such scratches, effects and the like will collectively be termed “defect portions”). In order to prevent such missing portions from arising, at the image reading device, when the image is read by infrared rays, only the portions at which light scatters due to these defect portions are detected. The missing portions of the image at these defect portions are, at a central processing unit, subjected to image processing for digital correction on the basis of the image information of the region at the periphery of the defect portion.
In such an image reading device, it has been thought preferable to improve the read image quality by using, for the light source of the optical system, a quaternary LED light source rather than a ternary LED light source, in order to improve the read image quality.
Thus, by changing the 650 nm wavelength of light emitted by the R color LED elements in a ternary LED light source to a 630 nm wavelength of light emitted by the R color LED elements in a quaternary LED light source, an attempt has been made to improve the image quality of the image read by the image reading device.
However, the light emitted by the R color LED elements in a quaternary LED light source includes sub-emitted light in a vicinity of the wavelength of 860 nm which is the secondary peak wavelength, i.e., includes infrared rays which are invisible light.
There is hardly any difference between the transmittance of this sub-emitted light with respect to the deep colored portions of the image of color wavelengths (i.e., wavelengths in the visible light region) of the photographic film, and the transmittance of this sub-emitted light with respect to the pale colored portions. Thus, the problem arises that the device will not be able to accurately read the degree of contrast in the image information of red wavelengths in the visible light region of the image.
Thus, in an optical system of an image reading device using quaternary LED elements as the light source, it has been thought to remove the sub-emitted light, which is infrared rays in a vicinity of a wavelength of 860 nm which are emitted by the R color LED elements, by mounting an infrared ray filter to the light source. However, the infrared rays which are in a vicinity of a wavelength of 950 nm, which are emitted by the plural infrared ray (IR) LED elements distributed and arrayed on the substrate of the quaternary LED light source, are simultaneously cut by the infrared ray filter.
Thus, there is the problem that, even when defect portions exist on a film, when the image is read as described above, it is not possible to detect the portions where light scatters due to the defect portions, and is not possible to carry out processings such as image correction and the like.
Further, quaternary LED light sources generate heat at the time of emitting light. Thus, as a measure to dissipate heat, the LED elements have been mounted to an aluminum or ceramic substrate. Therefore, the problem arises that the light source becomes expensive.